In face milling operations, in particular of engine blocks made of cast iron and having a width of their face surface less than the diameter of a face milling cutter, there exists a so-called `frittering` or `chipping` problem connected with the fact that an uncut portion of the workpiece adjacent the workpiece edge, which is continuously decreasing in size upon an operative cutting insert approaching the workpiece edge, is sheared off when the size thereof becomes so small that it can no longer resist cutting forces acting thereon. Thereby, the quality of the machined surface adjacent the workpiece edge is essentially deteriorated.
To reduce the above effect, there is provided a cutting insert having main and minor cutting edges which merge via a corner portion of a relatively large radius. As illustrated in FIGS. 1a and 1b, with the radius of the operative corner portion A being relatively large, a lead angle B at which the insert cutting edge C is inclined with respect to the workpiece face W is continuously reduced upon the cutting edge approaching the workpiece edge D. By virtue of this, cutting forces acting on the uncut portion E of the workpiece are reduced and the danger of `chipping` is decreased.
It is the object of the present invention to provide a new cutting insert enabling a further diminishing of the `chipping` effect and this without sacrificing the insert's service life.